1. Field of the Invention
The present invention relates to a data communication system which is capable of executing data exchange between plural networks by connecting the plural networks, to which node terminals are connected respectively, via relay units and, more particularly, a data format for use in a communication system in which respective routes of communication data as transmission objects can be arranged by use of root addresses which are constructed by arranging addresses of the relay units existing at branch points of the communication routes in passing order.
2. Description of the Prior Art
In the prior art, as disclosed in Patent Application Publication (KOKAI) 59-62245, for example, a data communication system has been widely known in which a plurality of local area networks (referred to as "LAN's" hereinafter) used to execute data exchange between a plurality of stations are connected via gate ways to enable data exchange between LANs.
According to the technology disclosed in the above Publication, in addition to transmitter/receiver addresses for designating the transmitter and the receiver of data respectively, a transmitting or receiving station address indicating the data transmitting or receiving station and a network address indicating the network to which the data transmitting or receiving station belongs have been provided in the transmitter/receiver addresses of the communication data. Hence, even if data communication is to be carried out beyond its own network, certain data communication between different LAN's has been made possible by referring to these addresses upon data communication.
However, according to the addressing approach in the above data communication system in the prior art, the network address designated as the destination and the network address peculiar to the LAN in which the communication data exist have been compared with each other, and then it has been decided timely, based on whether or not these addresses coincide with each other, whether or not the communication data have reached the LAN as the destination. Therefore, for example, at the time when communication is carried out between the LANs with the intervention of one or more than two LANs in the communication routes, in case the routes branch off to plural routes with the travel of the communication data, the above communication system has not been able to decide which branch routes the communication data should be supplied to, so that the communication data have reached the destination LAN while taking a detour of the route. As a result, such a problem to be solved has been involved in the prior art that it is difficult to increase data transmission capability per unit time.
Moreover, according to the addressing approach in the above communication system in the prior art, at the time when various addresses including the transmitter/receiver addresses, a transmitting or receiving station address, network addresses, etc. are allocated to the communication data, procedures of writing various addresses in the small address area has not been mentioned, so that there has been such a tendency that the address area used to write various addresses is expanded. As a result, the same problem to be solved has also been involved in the prior art that it is difficult from this respect to increase the data transmission capability per unit time.